A self-doping type electroconductive polymer is generally soluble in water and has characteristics of being easily formed in an arbitrary shape, formed in a film or positioned, and is therefore characterized with its extremely excellent workability in preparation of a large-area film or in an electrical device requiring microfabrication technology.
A charge-up preventing technology utilizing such characteristics in a lithographic process employing charged particle beams such as electron beams or ion beams is disclosed (JP-A No. 4-32848) and is being widely employed recently.
A chemically amplified resist, which is an essential material in common technology for lithography utilizing light or charged particle beams such as electron beams or ion beams, is a resist which is easily influenced by the use environment and is difficult to handle.
In case of coating a surface of the chemically amplified resist with an electroconductive composition, it is already known that a slight acid component in the coating material can have a significant influence on the sensitivity of the resist. That is, phenomenons that under a certain hydrogen ion concentration (pH) range, acid generated by exposure is neutralized by the coating material and that acid supplied from the coating material makes an unexposed part fall in the same state as an exposed part are observed. Such a phenomenon appears as a film thickness loss in case of a positive type resist, while in case of a negative type resist, such a phenomenon appears as formation of a hardly soluble layer or an insoluble layer.
For suppressing a pH change in an aqueous solution of an aqueous solvent-soluble electroconductive polymer, there is disclosed a method of eliminating oxygen dissolved in the solution (JP-A No. 8-259673) and a method of suppressing a pH decrease by using a buffer solution containing a weak acid and an amine (JP-A No. 11-189746).
Recently there is encountered a problem of resist collapse, caused by reduction in the minimum circuit line width of a semiconductor device, and attempts are being made to select an appropriate aspect ratio in order to avoid such phenomenon, whereby resist film thickness tends to become smaller. A resist patterned through a developing step is subsequently used for a pattern transfer to a substrate by a dry etching step, and dry-etching resistance of the resist in this process is becoming more important, so that requirements for the prevention of a film thickness loss phenomenon of the resist caused by a charge-up preventing film and for the maintenance of a resist profile are becoming stricter in recent years.
More specifically, in a process of forming an antistatic treatment film on a resist surface, in case where a solvent having a high affinity with water contained in the antistatic treatment agent remains in the resist, the liquid components show mutual penetration. As the aqueous solvent-soluble electroconductive polymer also migrates with the penetration of the liquid components, a mixing layer is formed at the interface between the resist and the antistatic treatment film. When the concentration of an acid component derived from the aqueous solvent-soluble electroconductive polymer contained in the mixing layer exceeds the concentration inducing a chemical change of the resist, there is exhibited a film thickness loss phenomenon in case of a positive chemically amplified resist, or formation of a hardly soluble layer or eventually a fogging phenomenon in case of a negative chemically amplified resist. Such an undesired chemical change at the interface generates a profile called a bowing or a T-top in the resist after patterning. In the process of transferring such pattern onto a substrate such as a silicon wafer, the development of such profile detrimentally affects control of variation in the line width and the depth and shape of etching, thus constituting a serious problem in fine patterning.
It is known that since chemical amplification resists are mostly oil-soluble and a coated film thereof is not easily mixed with water, in case of coating a resist surface with an electroconductive composition, a surfactant is added to the electroconductive composition for the purpose of improving a wettability. However conventional surfactants that have been employed often cause an influence on the resist profile such as film thickness loss of the resist, while decrease in the amount of the surfactant reduces the wettability, thus affecting the coating property. On the other hand, since the surfactant also has an influence on the resist, there is disclosed a method of utilizing a water-soluble polymer having a surfactant effect (JP-A. No. 2002-226721).